Diphenhydramine Flashcards
Please note that the drug card information is for Educational Use ONLY, and the source is from Carrie Bowman's glossary of drug cards permitted by use of Georgetown NAP students. No permission is given to use these cards for anything other than as a study resource for our program.
What is the trade name for diphenhydramine?
Benadryl
What drug class is diphenhydramine in?
First generation antihistamine/ H1-receptor antagonist
What are the clinical uses of diphenhydramine?
- Prevent or treat allergic/hypersensitivity reactions to other drugs, blood products, or common allergens; given along with epinephrine in anaphylaxis
- Treatment of motion sickness, parkinsonism, sedative/mild hypnotic, antiemetic
- antipruritic, antitussive, anticholinergic, antinausea and topical anesthetic properties
- treatment of antipsychotic induced extrapyramidal symptoms
What is diphenhydramine usually given in combination with for prophylaxis?
Cimetidine (H2-antagonist) and steroids for prophylaxis in patients with chronic atopy (hereditary predisposition to developing allergies), latex allergy, and before chemonucleolysis and dye studies which are known to be associated with allergic reactions
What is the MOA of diphenhydramine?
-Blocks Histamine-1 receptor by competing with histamine on the effector cell receptor sites, thus preventing the effects of histamine peripherally
Where are the effector cells (that have H1 receptors) for Diphenhydramine?
effector cells for this medication are in the GI tract, blood vessels, and respiratory tract
What is the onset and duration of action of diphenhydramine?
Onset: RAPID
DOA: 4-6hours
What is the half-life of diphenhydramine? what is different for the elderly?
- 2-8hrs
- 13.5 hours in the elderly
How is diphenhydramine metabolized?
Extensive hepatic metabolism with smaller degrees in the pulmonary and renal systems; SIGNIFICANT first-pass effect
What is the elimination route for Diphenhydramine?
A portion of the drug is excreted unchanged in the urine
not much info on extensive pharmacokinetics
What is the Volume of Distribution of diphenhydramine?
widely distributed in the body, and its distribution includes the CNS
Is diphenhydramine protein bound, if so how much?
78% protein bound
What is the Bioavailability of oral diphenhydramine?
40-60%
What are the side effects of diphenhydramine?
- moderate somnolence, drying of nasal mucosa, dry mouth
- Hypotension, dizziness, tachycardia, urinary retention, seizures, epigastric distress, thickening of bronchial secretions, irritability, constipation
- nervousness, fatigue, photosensitivity, N/V, wt gain, anorexia, hemolytic anemia, thrombocytopenia, agranulocytosis, tremor, palpitations, paresthesia, blurred vision, disturbed coordination, paradoxical excitement, insomnia, euphoria, confusion, rash, angioedema, diarrhea, urinary frequency
- seizures
What is different regarding adults and pediatric populations vs young pediatric populations as side effects of diphenhydramine? what about elderly patients?
- in adults and pediatric patients, this drug can cause decreased alertness, while in YOUNG pediatric patients it may produce excitation
- elderly patients more likely to cause dizziness, sedation, hypotension
What can diphenhydramine administration do with your anesthesia?
Due to sedative side effects, administration immediately before end of anesthesia may delay recovery
What are the contraindications to diphenhydramine?
- all first generation H1 receptor antagonists are contraindicated for use when DRIVING or operating heavy machinery
- This drug is contraindicated in premature infants, neonates, or nursing mothers
- dont use as local anesthetic
- dont give to ppl with known hypersensitivity reaction
Why should you NOT use diphenhydramine as a local anesthetic?
due to the risk of local necrosis!
When should you use CAUTION with diphenhydramine?
-use with caution in pts with lower respiratory disease, increased IOP, hyperthyroidism, CV disease, hypertension, narrow-angle glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction, symptomatic prostatic hypertrophy, or bladder neck obstruction
What does diphenhydramine do to the hepatic enzymes? Which enzymes?
Moderately inhibits CYP2D6!!!!!
What drugs does diphenhydramine have additive effects with?
Alcohol and other CNS depressants
What drug can intensify and prolong the anticholinergic effects of diphenhydramine?
MAOIs
Co-administration with any of these drugs (3) can cause anticholinergic syndrome
Amantadine
Rimantadine
Anticholinergic drugs
What can diphenhydramine cause with beta blockers (such as atenolol)
increase the bioavailability of atenolol
What do cholinergic agents do to the effects of Diphenhydramine?
(includes donepezil, rivastigmine, and tacrine) cholinergic agents antagonize the therapeutic effects
What can diphenhydramine do to Digoxin and/or levodopa?
May decrease gastric degradation and increase the amount of digoxin and levodopa absorbed by delaying gastric emptying!
What does administration with diphenhydramine and neuroleptics do?
therapeutic effects may be antagonized
What herbs/nutraceuticals should you avoid with diphenhydramine? why?
Valerian, St Johns Wort, Kava Kava, Gotu Kola
-may increase CNS depression
What is the IV dosage of diphenhydramine?
10-50mg IV q6-8hrs
What is the oral dosage of diphenhydramine?
25-50mg oral q6-8hrs
What is the available IV concentration of diphenhydramine?
IV form is available in concentration of 50mg/mL with a pH adjusted to a range of 5-6
